Source for vapor deposition



Sept. 1, 1959 Filed Feb. 3, 1958 R. A. GUDMUNDSEN ETAL SOURCE FOR VAPORDEPOSITION 2- Sheets-Sheet l Jon H. Myer, I

Richard A. Gudmundsen, INVENTORS.

A TTORNEY.

p 1959 I R. A. GUDMUNDSEN ETAL 2,902,574

SOURCE FOR VAPOR DEPOSITION Filed Feb. 3, 1958 2 Sheets-Sheet 2 F fg. 6.

Jon H. Myer,

Richard A. Gudmundsen,

INVENTORS.

A T TOR/VE Y United States Patent Office 2,902,574 SOURCE FOR VAPORDEPOSITION Richard A. Gudmundsen, Rolling Hills, and Jon H. Myer,

Los Angeles, Calif., assigno'r'sto Hughes Aircraft Company, Culver City,Calif., a corporation of Delaware Application February 3, 1958, SerialNo. 712,913 Claims. :1. 2219-19 This invention relates to vapordeposition and more particularly to an improved source from which arelatively thick layer of molten material may be deposited byevaporation upon a surface to be coated.

In the prior art wherein a layer of molten material is to be depositedupon a surface by evaporation of the material from a source, diflicultyhas often been encountered when it becomes desirous to depositrelatively thick layers by the methods heretofore known. For example,vapor deposition of materials in the prior art has generally beenperformed by resistance heating of a wire filament of variousconfigurations. Such a filament works well so long as relatively thinlayers of material are deposited. When thick layers of material arerequired and the amount of material placed upon the wire filament isincreased to accomplish this, it has been found that the material to bedeposited upon becoming molten tends to fall or drop from the filamentprior to evaporation thereof. This, therefore, limits the amount ofmaterial which may be placed upon the wire filament and in turn limitsthe thickness of the moltenlayer of material which may be deposited uponthe desired surface. It has also been found in many instances that thethickness of the layer of material deposited upon the desired surface isnot uniform.

A further consideration of prior art methodsis that when evaporatingfrom a wire filament or the like the vaporized material leaves thefilament in a non-directional manner. Such evaporation tends to coat theinterior surface of the chamber within which the evaporation is takingplace, thus resulting in a great loss of material.

Accordingly, it is an object of the present invention to provide asource for vapor deposition of relatively thick layers of material upona desired surface.

It is another object of the present invention to provide a source fromwhich material may be evaporated to provide relatively thick layersthereof upon a desired surface and from which the material to beevaporated will not drop prior to evaporation thereof.

It is still another object of the present invention to provide a sourcefrom which material may be evaporated and which is capable of retaininglarge amounts of material and from which the material may be evaporatedevenly over the surface upon which it is to be deposited.

A still further object of the present invention is to provide animproved source from which material may be deposited in substantiallythick layers upons urfaces to be coated therewith which is adapted forproduction processes and which is rugged in construction.

Yet another object of the present invention is to provide a source fromwhich material may be evaporated in a controlled and predetermineddirection.

An improved source for vapor deposition of a material upon a surface tobe coated therewith in accordance with the present invention comprisesa'member of heat conducting material having an orifice in the surfacethereof which, is disposed in a predetermined direction, at least onecavity is provided within said member for receiving 2,902,574 I PatentedSept. 1, 19 59 2 a material which is to be deposited, the orifice andthe cavity being in communication with each other.

The novel features of the present invention are set forth in theappended claims. Further objects and advantages of the present inventionwill be better understood from the following description taken inconnection with the accompanying drawings in which alternativeembodiments of the present invention are illustrated by way of example.It is to be expressly understood however that the drawings are for thepurpose of illustration and description only and are not intended as adefinition of the limits of this invention.

Fig. 1 is a schematic diagram partly in cross section of one form ofapparatus in which the present invention may be employed.

Fig. 2 is a top view of one embodiment of a container in accordancewiththe present invention.

Fig. 3 is a schematic diagram of a cover or cap for the container asshown in Fig. 2. t

Fig. 4 is a cross sectional view of the container as illustrated in Fig.2 taken about lines 44.

Fig. 5 is 'a schematic diagram partly in cross section illustrating thecontainer as shown in Fig. 2 fully assembled and in operation.

Fig. 6 is a side view partly in cross section of an alternate embodimentof a container in accordance with the present invention.

Fig. 7 is a top view of the container of Fig. 6 illustrating thearrangement of cavities therein.

Fig. 8 is a cross sectional view of the container illustrated in Fig. 6taken about the lines 88.

Referring now to the drawings wherein like reference charactersdesignate like or corresponding parts throughout the various views,there is shown in Fig. 1 one form of apparatus for depositing a materialsuch as molten metal upon the surface of a semiconductor body which isillustrative of the applicability of the present invention. For example,in forming a P-N junction upon a silicon semiconductor body inaccordance with the method disclosed and claimed in Patent No.2,789,068, issued April 16, 1957, to J. Maserj ian, a silicon body ispreheated to a temperature above the eutectic temperature of silicon andaluminum and a molten layer of aluminum is deposited upon the siliconsurface. The heating of the body and the evaporation of the aluminumupon the surface thereof is performed in an inert atmosphere or avacuum. The apparatus as shown in Fig. 1 may also be used to evaporate ametal such as gold upon the surface of a semiconductor body to providean ohmic connection thereto. Although the applicability of the presentinvention will be discussed with respect to deposition of metal upon asilicon semiconductor body, it is to be expressly understood that manyother materials may be deposited from the source of the presentinvention. An example of additional materials is compounds or oxides ofvarious material, such as those used in lens coatings, surfaceprotection and shadow casting for electron microscope work.

Referring now more particularly to Fig. l, the apparatus for carryingout a process as described above is shown and comprises a vacuum chamber11 defined by a bell jar 12, and a base 13, a port 14 communicates withthe vacuum chamber 11 and is attached to a vacuum pump 15. A resistanceheating platform 16 is sup ported within chamber 11 by any means knownto the art, not shown for purposes of clarity. Platform 16 is connectedoutside the vacuum chamber to a source of electrical energy 20 by meansof leads 17 and 18. The source of electrical energy 20 maybe any typepresently known to the art which is controllable for supplying apredetermined amount ofelectrical energy to platform 16 and ispreferably of a type to supply a low-current at high voltage. It may,for example, include an 3 auto-transformer which is connectable across a110 volt alternating current source.

Positioned within vacuum chamber 11 is a container 21 constructed inaccordance with the present invention. Container 21 is connected toanother source of electrical energy 2%), which is preferably of a typeto supply a high current at low voltage, by means of leads 22 and 23. Asillustrated in Fig. 1, container 21 comprises a resistance heatedcontainer. It is, however, to be expressly understood that container 21may be heated indirectly as well as by means of passing an electricalcurrent therethrough.

Container 21 in its presently preferred embodiment, as shown in Fig. 2,comprises a member of heat conducting material, a recess 31 is providedalong a portion of the surface thereof which is adapted to receive acover or cap 32 as illustrated in Fig. 3. Slideable clamps 33 areprovided for retaining cover 32 in place as hereinafter more fullydescribed. The surface of container 21 defines an orifice therein asshown at 34 in Fig. 2. Orifice 34 extends from the recessed portion 31through the opposite side of container 21 as more clearly shown in Fig.4. Also provided within container 21 is a plurality of cavities 35spaced along the length of the container. The number of cavities isdetermined by the amount of material to be deposited and the surfacearea to be covered and, therefore, may be as few as one, there being noupper limit. Web 36 separating the cavities from the orifice is recessedalong the top surface thereof as more clearly shown in Fig. 4 to providedirect communication between each cavity and the orifice 34. Although itis not deemed necessary, a rib 37 is Provided between the outer wall ofcontainer 21 and the interior thereof in order to provide structuralstrength to con tainer 21, thereby making it more rugged in constructionand thus better adapted for utilization in production techniques.

In order to further illustrate the utility of the present invention, theoperation of the apparatus of Fig. 1 will be further described inconjunction with the formation of an ohmic contact by depositing a layerof molten gold upon a semiconductor body. With the bell jar 12 removed,a semiconductor body 45 is placed upon resistance heating platform 16,particles of gold 41 and 42 are placed within cavities 35 of container21 as shown in Fig. 5. In a typical example for providing an ohmiccontact to a silicon crystal a container having twelve cavitiesdistributed along its length may be used. About 2.7 grams of gold wouldbe distributed evenly in each of the twelve cavities. The specificamount of material to be used in any particular application is dependentupon the surface area to be coated and the thickness of material to bedeposited. Cover 32 is then placed within recess 31 and clamps 33 arepositioned so as to retain cover 32 in place. Container 21 is thenplaced within chamber 11 and electrical connection made thereto. In thepresently preferred embodiment of the apparatus as shown in Fig. 1,container 21 may be held in place by clamps which also provide theelectrical connection and at the same time allow container 21 to beadjusted in such a manner that the orifice is disposed in a downwarddirection towards semiconductor body 45. Container 21 is positionedabove the upper surface of the body 45 as shown in Fig. 1. The distancebetween the upper surface of body 45 and container 21 is not criticaland may vary depending upon the particular design considerationsinvolved in each application.

Bell jar 12 is then placed upon base 13 and the chamber 11 sealed bymeans of gaskets 24 and chamber 11 is then evacuated. Current is appliedto resistance heating platform 16 from source of electrical energy 24)to raise it to the necessary temperature. After the heating platform hasattained the required temperature current is passed through container 21to raise it to a temperature suflicient to melt and evaporate the goldas shown in Fig. 5. In practice using a container 21 made of carbonapproximately /8 inch in diameter, approximately 300 amperes of currentare passed through container 21 until the surface thereof between clamps33 appears to be bright yellow in color indicating a probabletemperature for the container of more than 1250 C. At such a temperaturethe gold will become molten and will then pass into the vapor state thusleaving the cavities and being projected through the orifice as shown at42 in Fig. 5 upon the surface of semiconductor body 45. The temperatureis maintained for a time sufficient to evaporate the desired amount ofgold upon the surface of body 45, utilizing the material and containerabove referred to. If the temperature is maintained for approximately 10minutes, it has been found that approximately milligrams of gold persquare inch of surface area will be deposited. When the gold evaporatesand is deposited upon the surface of semiconductor body 45 to thedesired depth, the semiconductor body is cooled to form the ohmicconnection thereto.

Although a carbon filament was illustrated in connection with theapparatus of Fig. 1 for evaporating gold upon the semiconductor body, itwill be apparent to those skilled in the art that many other materialsmay be utilized for the container as illustrated. The considerationswhich must be made in choosing a material for the container are asfollows: the melting point of the container material must be greaterthan the melting point of the material to be deposited upon the desiredsurface and in some applications, such as evaporation of metal upon thesurface of semiconductor bodies, the material of the container must bechosen so as to prevent the intro duction of undesired contaminants intochamber 11.

It should be further understood that many modifications of the internalstructure of container 21 may be made without variation from the scopeof the present invention. As an example, an alternative embodiment of acontainer in accordance with the present invention is illustrated inFigs. 6 through 8.

Referring now more particularly to Fig. 6 there is shown a container 51having cavities 52 disposed therein. A cap 53 retained by clamps 54 isutilized to cover cavities 52 during the evaporation of materialtherefrom. Communicating with cavities 52 is an orifice 55 more clearlyillustrated in Fig. 7. As shown in Fig. 7, cavities 52 may be disposedon opposite sides of orifice 55 and in staggered relationship with eachother. As more clearly shown in Fig. 8, cavities 52 are disposed at anangle with respect to orifice 55. In practice particles 56 of metal tobe vapor deposited upon a desired surface are placed within cavities 52as shown in Fig. 8. Cap 53 is then placed upon container 51 and clamps54 positioned to retain it firmly in place. As hereinabove described,the temperature of container 51 is raised first above the melting pointof the material to be evaporated and maintained there until the materialwithin cavities 52 becomes molten. The temperature of the container isthereafter raised above the evaporation temperature of the material tothus evaporate material 56 causing it to pass from the cavities 52 andthrough the orifice 55 com municating therewith in a downward directionupon the surface of the material to be coated.

There has thus been described a container for evaporat ing material inrelatively thick and uniform layers upon a surface to be coatedtherewith which is capable of retaining large amounts of the materialsto be evaporated and of depositing said material in a predetermineddirection upon the surface to be coated while at the same timeeliminating dropping of the molten material prior to evaporationthereof.

What is claimed is:

1. In a system for evaporating a material upon the surface of a body tobe coated therewith, a container for vaporizing said material anddirecting it toward said body, said container comprising; an elongatedmember of heat conducting material, a slot provided laterally in andextending through said member to thereby provide first and secondopposed openings in the surface of said member, a cavity within saidmember adjacent said slot and providing a third opening within thesurface of said member and adjacent said second opening, said cavitycommunicating with said slot, and means for substantially sealing saidsecond and third openings.

2. In a system for evaporating a material upon the surface of a body tobe coated therewith, a container for vaporizing said material anddirecting it toward said body, said container comprising; an elongatedmember of heat conducting material, a plurality of cavities disposedwithin and longitudinally along said member and adapted to receive saidmaterial, each of said cavities forming a first opening Within a surfaceof said member, a slot provided laterally in and extending through saidmember to thereby provide second and third opposed openings within asurface of said member, each of said cavities communicating directlywith said slot, and means for substantially sealing said first andsecond openings.

3. In a system for depositing a metallic material upon at least onesurface of a semiconductor body, a container for vaporizing saidmaterial and directing it toward said semiconductor body, said containercomprising; an elongated member of electrical and heat conductingmaterial, a plurality of cavities disposed within and longitudinally ofsaid member and adapted to receive and to retain said material prior toevaporation thereof, a slot disposed within and extending through saidmember to provide first and second openings therein and communicatingdirectly with said cavities, and a cover for substantially sealing saidcavities and said first opening, said second opening being positionedtoward said body, whereby said material upon vaporizing is directedthrough said second opening and toward said semiconductor body.

4. In an evacuated system for depositing a metallic material upon asemiconductor body, a container for vaporizing said material anddirecting it toward said semiconductor body, said container comprising;an elongated substantially cylindrical electrically and thermallyconductive member, a plurality of cavities within and disposed along thelength of said member and adapted to receive and retain said metallicmaterial prior to vaporization thereof, a slot within and extendingthrough said member to thereby provide first and second openings in saidmembers, said first opening being adjacent said cavities, said slotcommunicating directly with said cavities, and means for substantiallysealing said cavities and said first opening, whereby said metallicmaterial upon vaporizing passes from said cavities through said slot andaway from said member toward said body.

5. In an evacuated system for depositing a metallic material upon asemiconductor body, a container for vaporizing said material anddirecting it toward said semiconductor body, said container comprising;an elongated carbon bar, a plurality of cavities disposed within saidbar and tandemly along the length thereof for-retaining said materialprior to the vaporization thereof, a laterally disposed slot extendingthrough and providing first and second opposed openings in said bar,said first opening being disposed adjacent to said cavities andcommunicating therewith, a cover adapted to substantially seal saidfirst opening of said slot and said cavities to direct said materialupon vaporizing through said second opening of said slot in a downwarddirection toward said body, means operable for retaining said cover oversaid cavities and first opening, and means disposed upon said bar forproviding electrical connection thereto.

References Cited in the file of this patent UNITED STATES PATENTS2,439,983 Morgan et a1 Apr. 20, 1948 2,447,789 Barr Aug. 24, 19482,479,541 Osterberg Aug. 16, 1949 2,730,986 Patton Jan. 17, 19562,793,609 Shen et a1. May 28, 1957 2,812,411 Moles Nov. 5, 1957

